Development of speech motor control: Lip movement variability.

This study examined variability of lip movements across repetitions of the same utterance as a function of age in Swedish speakers. Subjects were 37 typically developed Swedish children and adults (19 females, 18 males, aged 5-31 yr). Lip movements were recorded during 15-20 repetitions of a short Swedish phrase using articulography, with a sampling rate of 200 Hz. After correction for head movements, the kinematic records were expressed in a maxilla-based coordinate system. Movement onset and offset of the utterance were identified using kinematic landmarks. The Euclidean distance between receivers on the upper and lower lips was calculated and subjected to functional data analysis [Ramsay etal., J. Acoust. Soc. Am. 99, 3718-3727 (1996)] to assess both temporal and spatial variabilities. Results show a decrease in both indices as a function of age, with a greater reduction of amplitude variability. [Work supported by grant 349-2007-8695 from the Swedish Research Council.].